1. Field of the Invention
The present invention relates to a method for applying an orthodontic adhesive to the base of an orthodontic appliance, and is especially suitable in the manufacture of packaged, adhesive precoated orthodontic appliances.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct positions. Tiny orthodontic appliances known as brackets are connected to anterior, cuspid and bicuspid teeth, and an archwire is placed in a slot of the brackets. The archwire forms a track to guide movement of the teeth to desired positions for correct occlusion. Often, the ends of the archwire are held by appliances known as buccal tubes that are secured to molar teeth.
In previous years, orthodontic appliances such as brackets and buccal tubes were connected to teeth by welding or brazing each appliance to a band that was then placed over the desired tooth in encircling relation. In more recent years, however, it has become common practice to bond orthodontic brackets directly to the surface of the tooth. Omission of the metal bands long associated with the brackets provides a more aesthetic appearance than the appearance of brackets welded to bands, and helps to alleviate the problem of the "tinsel tooth" or "metallic mouth" appearance that is often associated with orthodontic treatment.
For many years, it was common practice to apply orthodontic adhesive to the base of directly-bonded brackets immediately before the brackets and adhesive were placed on the tooth. In some instances, a quantity of the adhesive would be dispensed onto a mixing pad or dispensing well, and the orthodontist or the orthodontist's staff would then use a small spatula to "butter" each appliance with a small dab of adhesive. In other instances, the orthodontist or the orthodontist's staff would dispense a quantity of adhesive from a syringe onto the bracket base.
Recent advances relating to orthodontic appliances include adhesive precoated brackets such as are described in U.S. Pat. Nos. 4,978,007, 5,015,180 and 5,328,363. Adhesive precoated brackets typically include brackets upon which the manufacturer has applied a precise quantity of adhesive such as a photocurable adhesive. The adhesive is protected from light, evaporation, oxidation, contamination, humidity and sublimation by a release liner or outer package until use. When it is desired to mount the bracket on a tooth, the bracket is released from a release liner or coating (if provided) and then, with the adhesive, is simply placed directly on the tooth.
Adhesive precoated brackets provide a significant advantage to the orthodontist in that the orthodontist or the orthodontist's staff need not carefully dispense the adhesive through a syringe onto the base of each bracket, or alternatively need not dispense the adhesive onto a mixing pad or well and then carefully transfer the adhesive to the base of each bracket. Furthermore, the manufacturer can control the quantity of adhesive placed on each bracket. As a result, there is sufficient adhesive to substantially fill the space between the bracket base and the tooth when the bracket is pushed in position, and yet there is not an inordinate amount of adhesive such that excessive cleanup around the perimeter of the bracket base would be necessary. Advantageously, the adhesive is preferably a light-curable adhesive so that the bracket can be carefully positioned in a proper orientation on the tooth surface before a curing lamp is activated to cure the adhesive and securely fix the bracket in place.
One method of precoating orthodontic brackets with adhesive in automated fashion includes the use of an adhesive syringe that is activated by air pressure. The syringe is inverted and dispenses adhesive in such a manner that the adhesive hangs from the tip of the syringe by gravity. A bracket, carried by a bracket holder, is oriented such that the plane of the base of the bracket is vertical and the bracket moves in a horizontal direction toward a position next to a portion of the adhesive that is hanging from the syringe. Next, a pair of cutters, spaced vertically apart a distance that is approximately the height of the bracket base, are moved toward the bracket base and into the adhesive to cut a section of the adhesive. A blast of pressurized air is simultaneously directed toward the adhesive to push the cut section of the adhesive ribbon onto the base and also to blow the remaining, excess adhesive away from the bracket.
There is a continuing need in the art for improvements in the methods for precoating orthodontic appliances with adhesive. For example, it is desirable to increase the speed of the precoating method so that the manufacturing costs of procoating each appliance can be reduced. However, it is also important for each appliance to receive a precise volume quantity of adhesive to insure that the adhesive firmly affixes the appliance base to the tooth to avoid unintentional separation. It would also be advantageous to provide a precoating method that may be carried out in automated fashion with little, if any, attention by the operator.